Secondary electron emitting electrode



Feb. 13, 1940. I R WARNECKE 2,189,971

SECONDARY ELECTRON EMITTING ELECTRODES Filed Oct. 15, 1937 v COEFFICIENT OF SECONDARY ELECTRON EMISSION COPPER BERYLLIUM ALLOY 500 I I000 @500 p INVENTOR ROBERT WARNECKE BY ATTORNEY usual practice in electron multipliers to increase Patented Feb. 13, 1940 UNITED STATES PATENT OFFlCE SECONDARY ELECTRON EMITTING ELECTRODE Robert Warnecke, Paris, France, assignor to Compagnie Generale de Telegraphic Sans Fil,

a corporation of France Application October 15, 1937', Serial Ni), 169,172,

In France October 23, 1936 r 2 Claims. (Cl. 250-474) This invention relates to secondary electron emitting electrodesisuitable for use in so-called electron multipliers.

It is well known that most pure metals have rather slight secondary emission, and it is the the secondary electron emission by covering 'an ordinary metal electrodewith a layer of substance of more intense emission. For example, use has been made of a layer of a deposit of an alkali metal on an oxidised metal base, one

typical case being where caesium, oxide of caesium and silver are used.

ing good power of secondary emission while able to resist large rises of temperature.

In accordance with the invention use is made of a basis metal such as copper alloyed with a.

metal having low work function such as beryllium.

the above alloys is treated by heating in a high vacuum so as to drive off occluded gases. This process imparts a physical structure which greatly improves its secondary electron emission power. i

The proportion. of beryllium to the copper can be varied within fairly wide limits and maybe from 1% to 10% by weight of the alloy. 7

The accompanying drawing shows curves connecting the secondary emission factor n (ratio of the number of secondary electrons emitted per incident primary electron) with velocity v (abscissae) of primary electrons expressed volts. v

The curves I, 2, 3, 4 and'5 were obtained with An electrode made of or covered with one of an electrode of an alloy of copper and beryllium with 2.4% of beryllium; the curve I at ordinary temperature, the curve 2 at 700 C., the curve 3 at 800C and the curve 4 at 900 C. In each case the electrode was first thermally treated and de- 5 gassed as above stated.

Curve 5 was obtained for the same conditions as curve I that is to say cold, butafter 100 hours of operation.

Curve 0 is a curve for pure copper. 1O

These curves show that the secondary electron emissivity or multiplication effect does not;

exhibit appreciable fatigue and is practically independent of temperature up to about 1,000. The slight increase of the multiplication effect when 15 the temperature rises is probably attributable to the fact that the metal becomes gradually cleaner in proportion to the increase of temperature. l

The thermal treatment of the alloy for which curves I, 2, 3, 4, 5 were obtained, was carriedout as follows: the temperature was raised gradually (for about one hour) up to about 850 C. and

then maintained at this temperature for aboutv 2 /2 hours in a pressure below 8.10 mm. of mercury (during the first hour), the final pressur being less than 2.10-Tmm. of mercury.- I The power of secondary emission obtained is a little below that of electrodes covered with cer tain complex substances, but, on the other hand 30 the electrodes of this invention are moreeasy to manufacture and of much better thermal stability which last renders them very useful in high power v, tubes. i

i What I claim is:

1. A secondary electron emitting electrode for electron multipliers and the like having'asurface composed of an alloy of which the secondary electron emissivity is several times that of copper and is substantially independent of temperature and which consists of from 1% to 10% of berylliumand the balance of copper. 2. A secondary electron emitting electrode for 3 electron multipliers and the like having a surface of high secondary electron emissivity and composed of a copper beryllium alloy consist ing of 2 beryllium and the balance copper.

ROBERT WARNECKE 

